poj 3461 Oulipo (KMP入门）

Description

The French author Georges Perec (1936–1982) once wrote a book, La disparition, without the letter 'e'. He was a member of the Oulipo group. A quote from the book:

Tout avait Pair normal, mais tout s’affirmait faux. Tout avait Fair normal, d’abord, puis surgissait l’inhumain, l’affolant. Il aurait voulu savoir où s’articulait l’association qui l’unissait au roman : stir son tapis, assaillant à tout instant son imagination, l’intuition d’un tabou, la vision d’un mal obscur, d’un quoi vacant, d’un non-dit : la vision, l’avision d’un oubli commandant tout, où s’abolissait la raison : tout avait l’air normal mais…

Perec would probably have scored high (or rather, low) in the following contest. People are asked to write a perhaps even meaningful text on some subject with as few occurrences of a given “word” as possible. Our task is to provide the jury with a program that counts these occurrences, in order to obtain a ranking of the competitors. These competitors often write very long texts with nonsense meaning; a sequence of 500,000 consecutive 'T's is not unusual. And they never use spaces.

So we want to quickly find out how often a word, i.e., a given string, occurs in a text. More formally: given the alphabet {'A', 'B', 'C', …, 'Z'} and two finite strings over that alphabet, a word W and a textT, count the number of occurrences of W in T. All the consecutive characters of W must exactly match consecutive characters of T. Occurrences may overlap.

Input

The first line of the input file contains a single number: the number of test cases to follow. Each test case has the following format:

• One line with the word W, a string over {'A', 'B', 'C', …, 'Z'}, with 1 ≤ |W| ≤ 10,000 (here |W| denotes the length of the string W).
• One line with the text T, a string over {'A', 'B', 'C', …, 'Z'}, with |W| ≤ |T| ≤ 1,000,000.

Output

For every test case in the input file, the output should contain a single number, on a single line: the number of occurrences of the word W in the text T.

Sample Input

3
BAPC
BAPC
AZA
AZAZAZA
VERDI
AVERDXIVYERDIAN

Sample Output

1
3
0

   题意：在第二个字符串中查找第一个字符串出现的个数。
   以第一个字符串建立next函数，然后在第二个字符串中查找。
 

#include<cstdio>
#include<cstring>
using namespace std;
int next[100000];
char s1[100000],s2[2000000];
void get_next()
{
    int i=0,j=-1;
    next[0]=-1;
    while (s1[i])
    {
        if (j==-1||s1[i]==s1[j])
        {
            i++;
            j++;
            next[i]=j;
        }
        else j=next[j];
    }
}
int kmp()
{
    int i=0,j=0,k=0,len;
    len=strlen(s1);
    while (s2[i])
    {
        if (j==-1||s1[j]==s2[i])
        {
            j++;
            i++;
        }
        else j=next[j];
        if (j==len)
        {
            k++;
            j=next[j];
        }
    }
    return k;
}
int main()
{
    int n;
    scanf("%d",&n);
    getchar();
    while (n--)
    {
        gets(s1);
        gets(s2);
        memset(next,0,sizeof(next));
        get_next();
        int ans=kmp();
        printf("%d
",ans);
    }
}